Liquid pool cathode type discharge device with complementary baffle means



W- 7 J. L. ZEHNER L 3, 5,89 LIQUID POOL CATHODE TYPE DISCHARGE DEVICE WITH COMPLEMENTARY BAFFLE MEANS Filed Feb, 25. 1968 FIG.. 7 g

I "a fii" JAM ES L, ER,

ROBERT P. WATSON THE ATTORNEY.

United States Patent Ofiice 3,525,895 Patented Aug. 25, 1970 US. Cl. 3ll3--164 Claims ABSTRACT OF THE DISCLOSURE An ignitron for use in high vibration or shock environment including baflling means between the anode and the mercury pool cathode.

This invention relates to electric discharge devices and more particularl to are discharge devices incorporating liquid pool cathodes containing mercury.

Ignitrons are exemplary of arc discharge devices employing liquid pool cathodes containing mercury. The use of such devices in various applications, such as for example in portable welding controls, is limited somewhat by the mobility of the liquid pool cathode, since shock, vibration and/or change of orientation move the pool of mercury away from the ignitor, and in some cases either short circuits the device from cathode to anode or, if no mercury is present at the ignitor tip, may lead to nonoperation of the device.

It is an object of this invention to provide an improved ignitron for use in mobile or semi-mobile environment which are less susceptible to disruption of operation because of shock, vibration or change in orientation.

Another object of the invention is to provide an improved ignitron equipped with mercury pool battling means to prevent shorting of the anode by mercury splashing.

Still another object of the invention is to provide baflling means for an ignitron without presenting excessive impedance to electric current flow between anode and cathode.

It is a further object of this invention to provide an improved ignitron wherein short-circuiting between the pool cathode and the anode is largely prevented.

A still further object of this invention is to provide an improved ignitron wherein the ignitor firing circuit is protected from an over-voltage condition even when the mercury pool no longer is in contact with the ignitor structure and misfiring or non-firing is prevented.

Further objects and advantages of this invention will be apparent from the following detailed description thereof and from the appended drawings wherein FIG. 1 is a sectionalized elevational view of an electric discharge device incorporating an embodiment of the invention, and

FIG. 2 is an enlarged sectional view of the ignitor and cathode pool structure.

In the preferred embodiment of the invention as illustrated in FIG. 1, the electron discharge device comprises an elongated cylindrical envelope 1. The envelope 1 can be advantageously formed from stainless steel and includes inner and outer walls 2 and 3 respectively, defining a coolant chamber 4.

Envelope 1 is closed at its upper open end by a header assembly generally designated 5 which includes a customary anode seal construction. The header assembly 5 supports a generally cylindrical positive electrode or anode 6 centrally within the upper end of the envelope. As is well understood, the mentioned anode seal construction supports the anode 6 in insulated spaced relation with respect to the envelope 1 and provides an externally accessible anode terminal indicated by the numeral 7. The anode, in accordance with common practice in electric discharge devices of this type, may be formed of graphite.

The opposite end of the cylindrical envelope is closed by an inverted cup-shaped header 8 which is welded to the lower end of the inner cylinder 2 to form a hermetic seal. The negative electrode or cathode of the device is contained in an envelope and is provided by a pool of vaporizable liquid indicated by the number 10 which is usually mercury or a mixture or amalgam of materials including mercury.

In the operation of power conversion tubes or arc discharge devices of the described character, some of the cathode material 10 is ionized initially for example by starter electrode or ignitor 11 which is suitably supported on and electrically connected with conductive lead 12, sealed suitably through the header 8 and thereby made accessible for external electrical connection thereto of a starter circuit (not shown). Upon energization of the mentioned starter circuit the ignitor is effective for ionizing a small quantity of the mercury pool into which the ignitor 11 protrudes and thus an arc discharge is established between the surface of the cathode and the anode. The resultant arc discharge results in substantial mercury vaporization which in turn provides for a substantially increased current conduction. In order to maintain satisfactory operation of the device it is necessary that the mercury vapor pressure be maintained within a predetermined desired operating range. Otherwise arc-back or reversal of current How and the destruction of certain tube elements can result.

In order to maintain the mercury vapor within the desired predetermined operating range and in accordance with customary practice, a coolant such as water is admitted into the chamber 4 through an inlet 14a at the lower end of the chamber, circulated through the chamber and discharged through an outlet 14!) at the upper end of the chamber. By means of suitable temperature responsive means (not shown) the cooling effect is controlled to control condensation of mercury on the inner wall of the envelope and thereby control the internal mercury vapor pressure. The effectiveness of the arrangement in controlling the mercury vapor pressure is dependent upon the efiiciency with which the mercury is condensed.

It will be appreciated from the aforementioned description that the useful operation of the device of the aforementioned type is largely dependent on maintaining the cathode pool 10 in its desired location within the bottom of the envelope, irrespective of shock, vibration or changes in orientation of the device (within certain limits). Since in the operation and application of devices of this type, as for example in portable welding control devices, locomotives, etcetera, the orientation and vibration of the device cannot always be closely controlled, it is desired that the device he as independent of these criteria as possible. To this end there are provided in accordance with the invention, baflling means for maintaining the mercury pool in its preferred location, and/ or returning it to this location if displaced by undue vibration or change in orientation of the device. To this end a first baflle 20, which is of a generally cup-shaped annular element having a generally cylindrical wall portion 20a adjacent the wall 2 of the cylinder and a radially extending wall portion 20b adjacent the cathode pool level, is provided within the device. Complementary therewith there is provided a second bafile 21 which is a generally conically shaped and truncated annular element having a generally radially extending portion 21:: which is secured to the wall 2 of the ignition structure and a generally longitudinally extending cylindrical portion 21b spaced from the wall of the ignition cylinder and terminating generally above the cylindrically extending wall portion g 3 20a of the first bafiie 20 and surrounding the arc discharge area of the device. Bafiies 20 and 21 are secured in their respective locations by connectors 22 and 23 respectively. It will be apparent that first baffle 20 generally will eliminate minor ripples or waves caused in the mercury pool caused by agitation and vibration and tend to keep the mercury pool in its desired location, and more importantly, waves of mercury will not impinge directly on the vertical envelope wall causing splashing of the mercury throughout the tube. The openings in the bafiles should be as small as possible, consistent with the need for proper current flow between anode and cathode. Thus these openings should not be so small as to present excessive impedance to current flow.

Rapid tilting or change. of orientation of the ignition or sudden contact with another object may result in splashing of the mercury into the area above first baffie 20, which mercury will be generally splashed against the wall 2 of the cylinder and trapped by baffle 21. Baflle 21 is shaped to return the mercury to the lower part of the tube when the tube is returned to its vertical orientation. It will be seen that the volume capacity defined by the area between the baffles may be generally the same as the area defined by the pool in its desired location, such that orientation of the tube to a position 90' degrees from that shown will generally only result in displacement of the mercury pool into the area defined between the two baffies 20 and 21 unless accompanied by shock or vibration. When the tube is returned to its vertical position, the mercury will run down into its ordinary location. To this end the bafiies 20 and 21 are preferably constructed of a material which is not wet by the mercury, such as graphite, although other materials may be utilized for this purpose. Those ends of the bafiles directed toward the mercury pool should be pointed so as to prevent no perpendicular surface against which mercury may splash.

Retention of the mercury in the pool area of the tube is further enhanced by utilization of a series of fluid flow impedance means provided directly in the mercury pool area of the device. Thus, there is provided within the pool area several disk members 24, 25 and 26 which permit only impeded fiow of the mercury and rapid flow, which would result in splashing, is prevented. The number of impedance members may be varied to fill to the normal mercury level in the device. It will be appreciated that the impedance members 24, 25, 26 may alternatively be corrugated wire mesh or grids and any suitable configuration. In accordance with the preferred embodiment of the invention, member 24 is a corrugated metal disk while members 25 and 26 are wire meshes, preferably of molybdenum.

Under the extreme conditions contemplated for useof the device in accordance with the invention, it is possible that ignition of the arc may be attempted when there is no mercury in the pool of the device since the mercury is already dispersed along the walls of the tube. Under these conditions the device may not fire and harm to the ignition circuit from over-voltage may result unless a conductive path between the ignitor and the tube wall is provided. To this end there is provided in the base of the enclosure a dimple or depressed structure 27 which receives the end of the ignitor 11 as shown. The space between the ignitor tip 11a and the dimple 27 is filled with a wire gauze or mesh 28 which provides a high resistance conductive path to the wall of the device. Wire gauze 28 usually will retain sufficient mercury droplets to permit ignition of the device. Therefore, a misfire will not occur as when mercury is no longer present, and destruction of the ignitor circuit is prevented. The conduction path is of sufficiently high resistance that there is no interference with ordinary operation of the device when mercury is present. The gauze 28 is preferably of a material wet by mercury, such as molybdenum.

In the application of ignitrons of this type, strong pressures had developed to reduce the physical size of the devices and also to increase their portability. For example, in portable welding equipment it had been suggested that the ignitron co'ntactor be mounted directly on the transformers used in such applications. This change not only required compaction of the device :but required that the ignitrons be operable under severe conditions of vibration and shock, as for example when the transformer is swinging in air and comes in contact with some other object. Under such conditions, massive disruption of the mercury within the pool of the tube can be contemplated and ignitrons of conventional design are inoperable under such harsh conditions of use. It is seen from the above that, in accordance with the invention, there has been provided an ignitron which is completely satisfactory for use under such harsh conditions of vibration, shock and change in orientation of the device.

While the invention has been shown and described by way of specific embodiment thereof, it is not intended that the invention shall be limited to the particular form shown and described and it is intended that the appended claims shall cover all modifications thereof which lie within the true spirit and scope of the invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An arc discharge device comprising:

(a) an envelope (b) an anode'and a liquid pool cathode in said envelope (c) a pair of complementary bafile means mounted between the pool cathode and the anode (d) said bafile means being of complementary shapes whereby liquid displaced from the pool is readily returned thereto and which limit contact of the liquid with said anode (e) said bafile means comprising a first annular bafile adjacent the surface of the pool cathode and a second annular balfie intermediate the anode and said first baffle (f) said first baffle having a longitudinally extending wall portion secured to the envelope and a radially extending wall portion adjacent the pool cathode (g) said second baffle having a radially extending wall portion secured to the envelope and a longitudinally extending wall portion surrounding the arc discharge area between the cathode and the anode.

2. A device as recited in claim 1 and further including means for ionizing the material of said cathode to elfect an arc discharge between said anode and cathode, said ionizing means being supported adjacent a depression in said envelope with a tip portion thereof extending into said depression, and conductive mesh means between said tip portion and said depression.

3. A device as recited in claim 2 wherein said conductive mesh means is of molybdenum.

4. A device as recited in claim 1 wherein a fluid flow impedance member located within said pool cathode slows the movement of the liquid.

5. A device as recited in claim 1 wherein said bafiie means are composed essentially of graphite.

References Cited UNITED STATES PATENTS 1,244,483 10/1917 Farnsworth 313-164 X 2,175,894 10/1939 Hutchings 3l3171 X 2,189,635 2/1940 Klemperer 313-171 X 2,349,363 5/1944 Marshall et al. 313-171 X 2,437,146 v 3/1948 Zuvers 313204X 2,447,637 8/1948 Colaiaco 313-164 2,679,611 5/1954 Boyer 313 JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner US. Cl. X.R. 313171 

